Millions of Californians who contact the state’s new health exchange to buy insurance will be given the opportunity to register to vote, too, a move that some Republicans fear could benefit Democrats.

Secretary of State Debra Bowen made California the first state to designate its health exchange as a voter registration agency Wednesday, but others are expected to follow suit, said Shannan Velayas, Bowen’s spokeswoman.

“This is about making sure that all eligible Californians are offered the chance to register to vote,” Velayas said Thursday.

A 1993 federal law requires states to designate their agencies and offices that provide public assistance or disability services as voter registration agencies, Velayas said.

The federal law commonly is known as “motor voter” because it ensured that applicants for drivers’ licenses nationwide would be asked if they wanted to register to vote.

Public agencies in California that currently serve as voter registration outlets include the Department of Motor Vehicles and offices overseeing the state’s welfare, tax collection and in-home supportive services.

California’s health care exchange, Covered California, is creating a marketplace for millions of uninsured Californians to compare prices and buy health insurance policies this fall to take effect Jan. 1.

Many of Covered California’s clients are expected to be families of low and moderate incomes. Some will be eligible for taxpayer-subsidized policies, and others will have incomes low enough to qualify for Medi-Cal.

Senate GOP leader Bob Huff said he supports the notion of all Californians registering to vote but that targeting specific populations of people creates the possibility of partisan advantage.

“It does beg the question about whether it’s a systematic attempt to try to empower people more predisposed to vote their way,” Huff said of the designation by Bowen, a Democrat. “And that would be concerning to us.”

When the state launched an online system of voter registration two months before last year’s November election, the new voters who signed up were more Democratic than the voting population as a whole, according to an analysis by the California Civic Engagement Project at UC Davis.

Democratic Sen. Lou Correa of Santa Ana, chairman of the Senate elections committee, said he was not aware of Bowen’s designation of Covered California this week but supports the concept.

Lori Shellenberger, director of the Voting Rights Project of the American Civil Liberties Union of California, characterized Bowen’s designation as “one of the most significant voter registration policy decisions in the state’s history.”